Loop antenna



May 6, 1930.

s. E. ANDERSON LOOP ANTENNA Filed May 10, 1925 Patented May 6, 1930 NITED STATES SIDNEY E. ANDERSON, OF BROOKLYN, NEKV YORK, ASSIGNOR TO WESTERN ELECTRIC COMPANY, WCO-RPORATED, OF NET/V YORK, N. Y., A CORPORATION OF NEW YORK LOOP ANTENNA Application filed May 10,

This invention relates to loop antennae.

An object of this invention is to provide a novel and improved form of loop antenna wherein symmetry in the physical parts and more especially symmetry in the electrical characteristics thereof are secured.

Another object of this invention is to provide a loop antenna having high efiicie'ncy over awide range of wave lengths.

of improved devices associated with a loop antenna whereby rotation is permitted without affecting the physical or electrical symmetry, thereof.

A feature of this invention relates to an improved portable, rotatable loop antenna whereby strength and compactness are ob tained and whereby the conductors of the loop are held in equal spacing and under tension. 4

The antennaof this invention may (2011b prise a substantially rectangular loop formed with a plurality of equally spaced turns of a continuous conductor wound in solenoidal form about a supporting frame. The frame may, for example, comprise symmetrically intersecting arms of fullelliptical form rotatably supported by a circular base having contact member's arranged to n'a'ak'e continuous connection to a plurality of concentric rings connected to the loop conductor. The concentric rings are preferablyiarrangedin the same plane and so placed that the capacity between an outer ring and a common interme diate ring is equal to the capacity betweenan inner ring and the common intermediate ring. 7

By considering the following detailed description, in connection with theaccompanying drawings, a more comprehensive idea of the nature and advantages of this invention will he obtained. v

Fig. 1 of the drawings shows a frontview of one practical form of the loop antenna. Fig, 2 is a side. view ofthe antenna of Fig. 1. F 3 shows a front view of another type of loop antenna which embodies this invention. Fig. l is a detail view in section on line 4 of Fig. 5 showing the method of connecting'the loop conductors to the slip rings. Fig. is a An additional object concerns the provision 1923. Serial No. 637,941.

view cross section of the antenna base. Fig. 6 shows the arrangement of the slip rings. Fig. 7 shows the practical application of this invention to a radio receiving circuit. In F 1, a continuous conductor 10 which may be of the well known Lit-Zendraht wire is wound in equally spaced turns upon the frame 11. This frame comprises arms 12 and 13 intersecting at right angles, which arms may be constructed full elliptical form similar to a well linown type of vehicle spring; These arms are preferably ofinsn-- lating material, for example, birch or maple wood. They are fitted at their intersection by dovetailed construction and held place by attachment to a block 14- inserted in the common space between their sides. A circular plate 15 preferably of hard rubber is attached to the lower end of arm 12 of 11 as-s'hown. v u ponand is pivoted to an insulating base 16 which may, fer example, be birch orinaple weed. In crderte provide more ri" id con struction, a stiffeninginember l? w h may be alive'dg shaped post of birch Or maple weed fitted in the lower half? of arm 12'.

En 2 is shown a side view of the an tenn-a of ll illustrating the arrangement of the conductors 10 These conductors are carried in. equally" spaced grooves fo-r'm-ed on Plate 15 norm lay rests the outer edge of fanshapc'd plates 18 at'- v tached to the twoends of arm'f3" and the upper endof armlQ'. At the lower end of arm 12*,conduc tors 10 pass through equally'spaced holes 139 the fan-shaped plate 248 joining plate 15 to the lower end of arm "121 Plates l8" and 19 are preferably of insulating material w-hi'climay be, for example, phenol fiher'.

The conductor's ltlifo'rma continuous loop.

the-ends of which are conductively connected to suitableterminals 20 and 21 attached to the fiber plate 24 interposed between thecircular plate 15 a-nd the arm 12 as'shownin detailin Figs. 4 'a'nd5. The midpoint of loop c'onductors 106's conductively connected to a similar terminal 22'. Terminal21 is electrically connected to conducting piy'ot 2'5 of-Fi-g. 5. Terminal 20 connects to individual slip- 26 by way of h1g35 and screws 23' and 28 as shown in Fig. 1. Terminal 22 connects to slip ring 27 by way of lug and screws 33 and 38 in a like manner as shown in Fig. 5. Terminal 21 connects to pivot by way of a threaded projection 13 thereon screwed to lug 55. Screws 23 and 83 and pivot 25 serve also to fasten base plate 15 to fan-shaped plate 2 1. The slip rings 26 and 27 and the pivot 25, which may be of any suitable metal for example brass, are attached to the plate 15 concentric with pivot 25 which is at the center of the plate.

An antenna constructed in accordance with this invention having the following approximate dimensions has been found to operate satisfactorily over a range of wave lengths of approximately 600 meters in the neighborhood of 100 meters wave length.

The arms 12 and 13 are approximately thirty inches long making the loop 2 1 inches square. The fan shaped plates are approximately four inches wide at the outer edge, two inches wide at the inner end and one fourth inch thick.

Twelve turns of a continuous conductor of 81 strand No; 38 Litzendraht wire spaced five sixteenths of an inch apart composed the loop. r

In Fig. 3, a'form of loop antenna similar in construction to that of Fig. 1 is shown. The construction, differs, however, in that the arms 12 and 13 may intersect at angles other than right angles. The supporting member or post 17 in this instance is attached 5 to the frame 11 at a point between the arms 12 and 18 which are consequently. positioned obliquely thereto. The post 17 is so placed as to bisect the angle between the arms and is symmetrical with respect to'them.

The base plate 15 of this antenna is attached to the post 17 instead of to the arm 12 as in'the antenna of Fig. 1; In both anv tennae, the base plate 15 is so placed that its center is on the axial line of the frame and supporting post 17- and whereby a symmetrical structure is obtained.

Fig.5 shows also a cross-section of circular base 16 through the center of which is inserted cylindrical conducting bushing 30, which cooperates with pivot, 25.-- In base 16, parallel to the cylindrical bushing 30 are conducting brushes 34 positioned to make electrical connection with slip rings'26 and 27,

respectively.

f conducting mesh are held yieldingly in contact with rings 26 and 27 by individual springs 36', held in place by screws 40threaded to bushings 32 which encase the respective brushes and springs. Bushings 30 and 32 constitute. suitable terminals for connecting conducting'cord may pass. Base 16 contains :5 a hollow portion 11 to provide access to the Brushes 84, which may be of terminals 80 and 32 and to provide space for a conducting cord. If desired, however, a cord may be connected directly to the terminals 20, 21 and 22.

Fig. 6 is a plan view of plate .15 showing the arrangement of the slip rings 26 and 27 and pivot 25. One object of this invention concerns the novel arrangement of sliprings 26 and 27 and pivot 25 whereby the capacity between rings 26 and 27 is made equal to the capacity between ring 27 and pivot 25. The proper spacing of the slip rings and central pivot in order to obtain this balance of capacity may be calculated from the formula which is an expression for the capacity be: tween two concentric rlngs, where C is the capacity, K is the dielectric constant, R the radius of the outer ring and R the radius of the inner ring. In this formula it is apparent that if we wish to make the capacity between one pair of concentric rings equal to the capacity between another pair of cone centric rings of different radii, the ratio between the radii of each pair of concentric rings must be the same.

Referring to Fig. 6, R is the radius of the flange of the central supporting pivot 25, which constitutes one ring, R is the inside radius of inner ring 27 R the outside radius of inner ring 27, and R the inside radius of outer ring 26. The capacity between the two rings will thus be equal to the capacity between the inner ring andthe central pivot if the relation p I obtains. When the rings are spaced'in accordance with the above ratios a substantially exact balance between the capacity of the rings and the capacity of the inner ring and ingslip rings and brushes, therings have been placed one above the other .upon the extension of the shaft'supporting the loop. This form of construction, however. adds onsiderable bulk to. the antennae. It is one purpose of this invention to produce a portable antenna of as small size-as possible and the form of construction described accomplishes this purpose.

In Fig; 7 is shown a radio receiving circuit 2 with the loop antenna 50; of this invention connected to the detector D by a multiple conductor 51 for the purpose of receiving wave energy" The detector D comprises a three-electrode tube 52 having its grid-and filament connected to an input circuit conooI trical currents in the output circuit.

taining a polarizing battery 53, a portion of the turns of loop antenna 50, and one windin of transformer 54:. Generator 55 isassociated with the second winding of trans former 54 and supplies oscillations to the input circuit at a frequency different from that of the receiving waves whereby a beat or intermediate frequency is produced in detector D in amanner now well understood. The output circuit of the detector D comprises the plate of tube 52, primary winding of transformer 56, battery 57 and the filament of tube 52. The plate of tube 52 is also connected by way of a low capacity condenser 58 with a portion of the turns of loop antenna 50 which are in close induce tive relation to the portion associated with the amplifier input circuit. The condenser 58 is of such value as to balance'the internal grid-plate'capacity oftube 52 whereby undesired regenerative eflects, such as singing are prevented.

A variable condenser59 connected in parallel with the loop antenna forms a resonant, circuit therewith capable of being adjusted to the frequency of incoming electromagnetic waves.

For obtaining low frequency speech currents from the modulated intermediate frequency radio waves, a second detector D is associated with the detector D and the antenna 50 connected thereto, by means of an intermediate frequency amplifier IFA. Th intermediate frequency amplifier IFA receives energy from the output circuit of detector D through the transformer 56 and supplies energy through a resonant circuit 63 formed by a condenser and the primary winding of transformer 60, which resonant circuit is tuned to the intermediate frequency. The tuned circuit 63 serves to prevent the admission of extraneous frequencies into the input circuit of detector D.

The input circuit of detector D is supplied with waves of the intermediate frequency from the resonant circuit 63 through transformer 60; This input circuit contains in addition to the secondary winding of trans former 60, a grid lealr 61 consisting of a resistance and capacity in parallel.

A receiver 62 shunted by a condenser G l is connected to the output circuit of thedetector D for obtainin the reproduced signal speech sounds from'the demodulated elec- The condenser 64 offers low impedance to radio frequency currents but high impedance to audio frequency currents.

This system operates most successfully .1 when the circuits are electrically syminet ical with respect to ground. The loop antenna 50 maintains its capacity constant and balanced even when being rotated and thus prevents change of tuning or unbalance of the circuits. Hence, the use of a symmetrical loop antenna such as described herein is essential to the proper functioning of the circuit.

Although the principles of this invention have been illustrated and described in connection with certain specific structures, it is not intended that the present disclosure is to be limited thereto, but only in so far as pointed out in the following claims.

W hat is claimed is:

1. radio receiving system comprising a space discharge device having cathode, anode and control electrode, a wave collecting conductor comprisin a rotatable loop antenna having terminals connected respectively to said electroues through a plurality of slip rings, the portions of said conductor included between one of said terminals and the other two terminals respectivelybeing electrically balanced.

2. A radio receiving system comprising a space discharge amplifier having a cathode, anode and control'electrode, a rotatable loop antenna having a plurality of slip rings through which its outer terminals are connected to said anode and control electrode and an lntermediate terminal connected to sald cathode, the portion of said loop connected between the cathode and anode bein electrically balanced with respect to the por tion included between the cathode and con trol electrode.

3. The combination in a rotatable loop an tenna of a plurality of contact rings conductively associated with the turns of said loop, said contact rings being so arranged that the capacity. between one ring and each of the others is made equal.

4-. A radio receiving system comprising a space discharge amplifier having a cathode, anode and control electrode, a loop antenna provided with a plurality of slip rings, said slip rings being connected to end terminals and an intermediate.terminal of said loo and to the anode, control electrode, and cathode, respectively of said amplifier, said rings being arranged in such manner that the capacity of one with respect to each of the others is made equal. 1 5. in a symmetrical loop antenna, the comoination of'arotatable frame and a stationary base, said frame having concentric planar rings cooperating with contact members in said base, said contact rings being so spaced that the capacity between an intermediate ring and an inner and an outer ring is equal. 6. The combination in a rotatable loop antenna of a closed conductingloop having outer and middle terminals connected to individual slip rings on a supporting base said base having contact members cooperating with said slip rings, said contact members comprising conducting brushes slidably fitted V in a metallic bushing and yieldingly pressed against said slip rings under the action of a equal.

anode and control electrode, a rotatable loop antenna having equal portions connected between said cathode and anode, and cathode and control electrode, respectively, said portions cooperating with a balancing reactance to prevent singing in said amplifier and slip rings for effecting said connection whereby said antenna may be rotated without causing said amplifier to sing.

8. A loop antenna comprising a rotatable member, a stationary member, said rotatable member comprising a framework having full elliptical arms intersecting at right angles, a closed conducting loop supported by said frame, a circular base plate attached to the end of one of said arms, and a stiffening post fitted to the last mentioned arm, whereby said rotatable member may be rigidly supported.

9. A rotatable loop antenna, comprising a circular base, a rotatable frame mounted upon said base, a coiled conductor mounted upon said frame, and a plurality of concentric planar rings, said rings being connectively associated with the terminals of said coiled conductor and with a mid-tap thereto whereby electrical connection may be made to said loop during rotation and a balance in the electrical reactance of one of said rings with respect to the remainder thereof is maintained.

10. A loop antenna'of substantially rectangular form comprising a plurality of equally spaced turns of a continuous conductor, said conductor being supported upon a frame, comprising a pair of substantially elliptical trusses dovetailed at their respective midpoints and attached to arcentral block, whereby vibration of said frame is substantially prevented.

11. The combination with a radio receiving circuit of a space discharge tube having tinuous conductor, said winding being split by a mid-tap connected to an annular ring, said ring being connected to said cathode and associated with an inner and an outer ring connected respectively to said anode and control electrode and to respective terminalsof said winding and so arranged that the capacity between said first mentioned ring and said inner and outer rings respectively is 12. The combination in a loopaiitenna of a conductor coil in two sections, an insulating supporting frame and a base, said frame being rotatable upon said base and comprising means for making adjustable connection to the sections of said coil so that capacity balance between said sections is maintained.

13. A portable wave receiving device comprising a conducting loop, an insulating frame comprising full elliptical arms rotatably mounted upon a base having brushes cooperating with means associated with said arms for making connection to said loop, said means comprising a plurality of conducting elements, the capacity between adjacent pairs of elements being equal.

14; A loop antenna of substantially rectangular form comprising a plurality of 

